1. Field of the Invention
This invention relates to a digital content processing method, a valuable paper processing method and computer program product for processing digital content or valuable paper for secure distribution.
2. Description of the Related Art
Recently, the remarkable development of computers and networks has allowed many types of information such as text, images and sound, to be stored and processed using computers and networks. The above-mentioned types of information are generally stored as digital data, which is relatively easy to copy. Accordingly, it is common to embed copyright information or user information in digital data such as image data and audio data, in an effort to prevent illegal copying. Digital watermarks provide a system where specific data is secretly embedded in the image data or audio data using predetermined processing of the image data or audio data. It is then possible to obtain copyright information, user information or an identification number from the specific data and to identify a person or a product that made an illegal copy.
Ideal digital watermarks have several characteristics. First, the embedded information of the digital watermark should not be noticeable. In other words, the information should be embedded without degrading the quality of the original. Second, the embedded information should not be lost when editing or other processing such as data compression or filtering is performed. Third, the amount of information to be embedded should be variable. However these ideal characteristics of digital watermarks may be incompatible with each other. For example, in the case where a digital watermark is embedded in an image, the amount of embedded information needed to prevent loss of information during editing or processing of the image often degrades the image quality.
There are several known methods for embedding digital watermarks. Methods of embedding digital watermarks can be roughly categorized into two types: methods embedding information in a spatial area and methods embedding information in a frequency area. For example, “Techniques for Data Hiding,” Proceedings of the SPIE, San Jose, Calif., USA, (IBM) W. Bender, D. Gruhl and N. Morimoto, February 1995, and U.S. Pat. No. 5,636,292 describe two examples of methods embedding information in a spatial area. The following are a few examples of methods embedding information in a frequency area. A method using Discrete Cosine Transform is described in “Digital Watermark Method in a Frequency Area for Protecting Copyright of a Digital Image” (NTT) Nakamura, Ogawa, Takashima, SCIS'97-26A, January 1997. A method using Discrete Fourier Transform is described in “A Watermark Signature Method for an Image by Using PN Series” (National Defense Academy) Ohonishi, Oka, Matui, SCIS'97-26B, January 1997. Methods using Wavelet Transform are described in “Experimental Considerations Related to Safety and Reliability of Digital Watermark Technology Using Wavelet Transform” (Mitsubish, Kyushu University) Ishizuka, Ishi, Sakurai, SCIS'97-26D, January 1997 and “Digital Watermark Image Compression Based on Wavelet Transform, About Robusty for Conversing Process” (Matushita) Moue, Myazaki, Yamamoto, Katura, SCIS'98-32A, January 1998.
The above-mentioned digital watermark techniques may be used for copyright protection of digital content such as still images, moving images and audio. Additionally, digital watermark techniques can be used in preventing counterfeiting of money or valuable securities. However, even when the above techniques are used, it may still be possible to edit or process the digital content in order to intentionally pirate copyrighted digital content.
The complexity and capabilities of editing and processing techniques used for copyright piracy are constantly improving. An increasing number of people edit and process digital content in different ways for the purpose of illegally copying the content. It is difficult to develop digital watermark technologies that are capable of surviving all types of editing and processing.